The invention relates to immersive virtual reality systems.
As is known to those skilled in the art, immersive virtual reality systems are used more and more often in order to immerse users in virtual environments. This is the case particularly in, although not limited to, the field of vehicles, possibly of the automobile type. Such an immersion can be intended, for example, to teach a user to develop in a particular environment or to use objects or functions present in a particular environment, or to analyze the behavior of a user in a particular environment, or to observe a particular environment depending on the position of a user in relation thereto.
Usually, an immersive (virtual reality) system comprises:                at least one target capable of being connected to a user (or sometimes an object) which is capable of moving in a predefined space,        detecting means capable of detecting the current position of this target in this predefined space and of delivering a signal representative of this current position,        at least one displaying means responsible for displaying on at least one screen, installed in the predefined space, images (possibly three-dimensional (or 3D)) intended for this screen, and        processing means responsible for defining in real time for each associated screen three-dimensional (possibly stereoscopic) images of a chosen environment, depending on the current position of the at least one target and on the position of the associated screen in the predefined space.        
When a user uses such an immersive system, he quickly notices that there is a time difference or delay between the moment when he changes position and the moment when he sees each image that results from his change of position on each screen. This time difference or delay, commonly referred to as latency time, results from the processing times of the signals and data, the transmission times of the signals, data and images, the graphics rendering time of the computers and the time difference between the moment when the user finds himself placed in a new position and the moment when the detecting means detect the target (and therefore the user) in this new position.
Usually, the longer the latency time, the more uncomfortable the user, and the user may even suffer from nausea, dizziness or loss of balance. It is therefore important to know the (overall) latency time of an immersive system and, if possible, the main parameters that contribute thereto, if we wish to reduce the latency time to a value that is not uncomfortable for the user (i.e. that tends towards zero). Known solutions that enable the latency time to be determined, such as the one described for example in US Pub. No. 2015/097803, are not sufficiently precise and do not enable the main contributory parameters to be known.